Recently, measures for safety of an occupant of a vehicle have been actively considered. In order to protect the occupant sitting on the vehicle seat, a SRS (supplemental restraint system) such as an air bag is installed in the vehicle, and the number of the vehicles in which the SRS is installed has been increased. The air bag can increase its level of protective performance for an occupant in a case of an emergency in conjunction with the seat belt. In order to fully perform the protection of the occupant and to restrain excessive inflation, the air bag is controlled to inflate on the basis of an existence of an occupant sitting on the vehicle seat or a size of the occupant sitting on the vehicle seat. For example, the level of the inflation of the air bag is adjusted on the basis of the size of the occupant. Further, if an accident occurs when a child (for example, a child at young age) is sitting on the front seat, the air bag may injure the child because of an impact upon the inflation of the air bag. For such occasions, when the child is sitting on the front seat, for example, the air bag is controlled so as not to be actuated. In the light of this situation, an occupant detecting device may be provided at the vehicle seat in order to detect an occupant type seating on the vehicle seat on the basis of a size of the occupant.
For example, according to a vehicle seat apparatus and an air bag apparatus disclosed in JPH11-1153A, the weight of the occupant is detected first, and an amount of gas generated in order to inflate the air bag apparatus is controlled on the basis of the weight of the occupant. Specifically, load sensors for detecting the weight of the occupant seating on the vehicle seat are provided at the vehicle seat, and the amount of gas is controlled on the basis of the weight of the occupant detected by the load sensors. For example, four load sensors are provided under the vehicle seat at a front-right position, a front-left position, a rear-right position and a rear-left position. In this configuration, when the load sensors detect that the weight of the occupant is light, the amount of gas for inflating the air bag is reduced so that the inflation level of the air bag is restrained. When the load sensors detect that the weight of the occupant is heavy, the amount of gas for inflating the air bag is increased so that the inflation level of the air bag is increased.
As a measure of safety for an infant in a vehicle, use of a CRS (child restraint system) has been recommended. Actually, in some nations or regions of the world, use of CRS is required by law. As disclosed in JPH11-1153A, the occupant detecting apparatus for detecting the size of the occupant on the basis of the load applied to the vehicle seat calculates the load applied by the occupant to the vehicle seat as a total load applied by the child seat and the occupant. Further, a child seat for an infant is equipped with a belt by which the infant is secured, and the child seat itself is firmly secured to the vehicle seat and secured by means of the vehicle seat of the vehicle. In this case, because a tension of the seat belt is also considered as the load applied to the vehicle seat, a load that is larger than an actual load applied to the seat is detected. As a result, it may be difficult to control the air bag so as to be suitable for the infant.
Further, an occupant classifying device, by which the child seat secured to the vehicle seat is appropriately detected, has been disclosed in JP2001-294119A. The occupant classifying device includes a vehicle seat load scale and a human body contact sensor. The vehicle seat load scale measures the load applied to the vehicle seat, and the human body contact sensor detects a level of the contact of the human to the vehicle seat. By means of a combination of the vehicle seat load scale and the human body approaching sensor, an existence of the occupant sitting on the vehicle seat and an occupant type sitting on the vehicle seat are determined.
The occupant classifying device disclosed in JP2001-294119A detects a difference between the child seat and the child sitting on the vehicle seat. Accordingly, the occupant classifying device recognizes the occupant type (an adult, a child or an infant sitting on the child seat). In order to recognize the occupant type accurately, the load sensor (vehicle seat load scale) disclosed in JPH11153A needs to include a function of the human body approaching sensor disclosed in JP2001-294119A. In such configuration, the size of the device may be increased.
A need thus exists for an occupant classifying device which is not susceptible to the drawback mentioned above.